Unit 20 Magnetic Fields

9702

What is a magnetic field?

A region of space in which objects with magnetic properties/moving charges experience a force

What causes a magnetic field?

A moving charge or a permanent magnet

Which direction do magnetic field lines point?

North to south

What does the separation of the field lines represent?

Strength of the field

Define magnetic flux density

Force per unit length per unit current on a current-carrying conductor at right angles to the direction to the magnetic field. Units of Tesla (T).

When is the force on a current-carrying wire in a magnetic field 0?

When the current through it is parallel to the direction of the magnetic field

Give the equation to calculate the force on a current-carrying wire

F = BILsinθ

Describe Fleming’s Left Hand Rule

The thumb points in the direction of motion of the rod (or the direction of the force) (F). The first finger points in the direction of the external magnetic field (B). The second finger points in the direction of conventional current flow (I).

How can you increase the strength of a solenoid?

Increase the number of coils, place a ferrous material inside the coilG

Give the equation to calculate the force on a moving charge in a magnetic field

F = BQvsinθ

How do you find the direction a charged particle will move in a magnetic field?

Fleming’s Left Hand Rule

Define Hall voltage

The potential difference produced across an electrical conductor when an external magnetic field is applied perpendicular to the current through the conductor

What is a Hall probe

A device with a flat surface which magnetic field lines must pass perpendicular to

When is the Hall voltage at a maximum?

When the magnetic field is perpendicular to the probe

When is the Hall voltage at a minimum

When the magnetic field is parallel to the probe

Describe the motion of a charged particle in a magnetic field

Circular motion due to the force being at right angles to the direction the particle is moving

Give the equation to calculate the radius of the moving charge

r = mv/Bq

What is a velocity selector?

A device consisting of perpendicular electric and magnetic fields where charged particles with a specific velocity can be filtered

How does a velocity selector work?

Only particles with the correct velocity pass through the two fields undeflected. This velocity is the ratio of the electric and magnetic field strengths

Describe Fleming’s Right Hand (Generator) Rule

Used to predict the direction of the current caused by an induced e.m.f. in a conductor moved at right angles to a magnetic field

Define magnetic flux

The product of magnetic flux density normal to a circuit and the cross-sectional area of the circuit. Units of Weber (Wb).

Give the equation to calculate the magnetic flux

ϕ = BA

Define magnetic flux linkage

The product of magnetic flux for a circuit and the number of turns. Units of Weber (Wb).

Give Faraday’s law of electromagnetic induction

The magnitude of the induced e.m.f. is directly proportional to the rate of change of magnetic flux linkage

Give Lenz’s law

An induced e.m.f. is in a direction as to produce effects that oppose the change producing it

Give the equation for Lenz’s law

E = -ΔNϕ/Δt